Код:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" lang="ru" xml:lang="ru">
<head>
<title></title>
<style type="text/css">
* {
****margin: 0;
****padding: 0;
}
html, body {
****width: 100%;
****height: 100%;
}
#sidebar {
****width: 30%;
****height: 100%;
****background: #5F9EA0;
****float: left;
}
#header {
****width: 70%;
****height: 20%;
****background: #A294F3;
****float: left;
}
#content {
****width: 70%;
****height: 80%;
****background: #CEADAD;
****float: left;
}
</style>
</head>
<body>
<div id="sidebar">sidebar</div>
<div id="header">header</div>
<div id="content">content</div>
</body>
</html>